The invention relates to a particular structural configuration of an expansible mandrel for carrying spools and the like in winding machines. The spool serves as a carrier for the thread package to be formed on the winding machine.
Many varied constructions of expansible mandrels are known. The mandrels have an outer cover, subdivided by slots alternately opening in opposed directions. Thus, the cover surface may be radially inclined to clamp the spool pushed over the cover. that is, the cover surface exerts a radial pressure along the inside surface of the spool to hold it in place. The spool is mounted on the slotted cover generally by means of one or tow cones designed to run counter to one another. That is, there are two mutually opposed conical surfaces that are axially movable with respect to one another on the mandrel. This causes the cover surface to be spread radially so that the mounted spool is clamped and held secure by the spreading pressure.
Winding machines are operating at constantly increasing thread speeds. Thus, it is necessary to operate the expansible mandrel and spool at high rotary speeds. These rotary speeds may reach from 10,000 to 20,000 rpm. The high rotary speeds generate considerable centrifugal force which acts on the blade-like portions of the mandrel cover. The centrifugal forces cause bending stresses on the blades of the mandrel. Consequently, there is an involuntary raising of the blades above the spreading condition particularly when the spool has been weakened by damage. The spool may even tear as a result of this stress which can occur at the beginning of the winding procedure when an insufficiently strong thread package has been wound onto the spool. Radial bulging or breakage of the blade on the expansible mandrel can also occur. In this case, the cylindrical cover surface on the expansible mandrel is no longer present. Consequently, the winding procedure for forming a thread package is disturbed.